Method and apparatus for producing diffraction gratings by machine forming in a fast operation cycle

Abstract: A method and an apparatus for producing diffraction gratings by machine forming in a fast operation cycle, in which the forming of the grating grooves is provided by sizing a solid or added metal substrate (M) by means of a diamond point punching tool (A) driven at high speed by a piezo-electric actuator (P), the movement of which are controlled by an electronic and/or electro-optical high-precision system.

Description: The present invention relates to the field of the advanced optical technology and more particularly a method of producing diffraction gratings by machine forming in a fast operation cycle. This invention also relates to an apparatus for carrying out such method. It is known, from document EP 0169326, a process for the production of a macroscopic surface pattern with a microscopic structure, in particular a structure which has an optical-diffraction effect, by bulding selected surface regions of an embossing die having a microstructure into a thermoplastic layer, characterised in that a ray source is used to heat an approximately punctiform element of the surface of the thermoplastic layer. Said element lies in the focal spot of the ray source, so that the microstructure of the embossing die is plastically moulded only in said element of the surface of the thermoplastic layer, and that the surface pattern is composed of a plurality of such elements of the surface. In other words, said known process (and apparatus) is intended for embossing a pattern having a microscopic relief structure, such as an optical diffraction grating, onto a layer od thermoplastic material. Therefore, the method and apparatus disclosed in EP 0169326 are intended to plastically mould a thermoplastic layer having a predetermined optical diffraction grating, and are not able to create an optical diffraction grating. The present invention aims at providing a method and a device of the above-mentioned type for producing diffraction gratings in a considerably lower time than that required by the conventional mechanical and/or photomechanical techniques of the present state of art. According to the invention a method is provided consisting of the following steps: arranging a solid or added metal substrate on a displaceable means which moves at a controlled speed; and carrying out on said substrate a succession of sizing operations by a punching tool combined with a piezoelectric actuator so as to produce on said substrate a series of grooves forming the desired grating. Still according to the invention said punching tool is formed of a fixture provided with an active wedge-shaped diamond point having a rectilinear cutting edge arranged transversally to the displacement direction of the movable carriage of the substrate. This invention will now be described with reference to the accompanying drawings which show by way of an illustrative, non-limitative example a preferred embodiment of the invention. In the drawings: Fig. 1 is a schematic perspective view of the apparatus for carrying out the method according to the invention. Fig. 2 is a block diagram of the control assembly of the apparatus of Fig. 1. Figs. 3 and 4 show the results of some characteristic tests of the invention. With reference to Fig. 1, a wedge-shaped diamond point tool A machined with a determined angle is fixedly attached to a piezoelectric actuator P capable of carrying out a vertical micrometrically controlled displacement with a high repetition frequency. Diamond A is arranged with a horizontally aligned cutting edge S. Translation carriage C slides under tool A horizontally and transversally with respect to cutting edge S of the tool, said carriage carrying a metal substrate M having a surface B, on which the grating is cut, which has been formerly machined with optical finish and carefully positioned with respect to the edge of the tool. The combined movements of tool A and substrate M produces a succession of rectilinear, parallel cuts I (forming the grooves of the grating) spaced by a gap of p = v/f, where v is the sliding speed of substrate M, and f is the operation frequency of the piezoelectric actuator P. By varying v during the cutting step, gratings having varying spacing may be produced. Also the depth of cuts I can be varied by a suitable modification of the diamond point A and the operating characteristics of piezoelectric actuator P. A block diagram of the control assembly of the described apparatus is shown in Fig. 2. The invention allows a number of advantages to be achieved with respect to the already known techniques, among which a higher production speed which entails a considerable reduction of the cost of the end product, and a high capability of controlling the operating parameters with the result of a high flexibility as far as the type of the produced components is concerned. Fig. 3 shows two interference diagrams obtained by interferometer microscope and concerning the profile of gratings provided by the above-mentioned method, and Fig. 4 shows the profile of a grating detected by a mechanical high-resolution profilometer. The invention may be advantageously applied to the production of a large range of advanced optical components such as the diffraction gratings having varying spacing, which find application in the VUV spectroscopy and soft X-rays. Such gratings can be particularly used in the field of the analysis of the synchrotron radiations and in the space applications as well. The present invention has been illustrated and described with reference to a preferred embodiment thereof, however it should be understood that construction and/or operating modifications can be in practice made by those skilled in the art without departing from the scope of the present invention.

Claims: A method of producing diffraction gratings, comprising the steps of arranging the substrate, on which the grating grooves are to be produced, on a translation means, having a controlled speed of traslation, providing said grooves by repetitively punching with a tool moving with respect to the substrate; characterized in that: each step of punching comprises punching the substrate directly with a wedge-shaped diamond edge of said tool, while controlling the translation of the substrate with regard to said punching tool, so as to provide one groove at any stroke of the tool on the surface. A method according to claim 1, characterized in that the translational speed of the substrate can be changed during the translation of the substrate with respect to the punching tool so as to provide corresponding variations of the gap between the grating grooves. A method according to claims 1 and 2, characterized in that the punching tool moves vertically. A method according to claims 1 to 3, characterized in that the method comprises providing the punching tool with a wedge-shaped diamond edge having the edge arranged perpendicularly to the sliding direction of the carriage carrying the substrate. A method according to claims 1 to 4, characterized in orienting the substrate formed of a solid body and having a surface with optical finish so that said surface faces the punching tool. An apparatus for carrying out the method according to claims 1 and 2, where the apparatus comprises: a) a punching tool provided with a wedge-shaped diamond edge; b) a piezoelectric actuator arranged for driving the punching tool; c) an electronic assembly arranged for controlling the actuator; d) a translation system arranged for carrying the substrate; e) control means arranged for controlling the speed of the translation of the substrate, wherein the electronic assembly and control means are arranged so as to provide one groove at any stroke of the tool on the surface of the substrate. An apparatus according to claim 6, characterized in that said the electronic assembly is an electro-optical assembly.

Inventors: BOTTICELLI ANTONIO, CINTI MARIO, DE ANGELIS ALBERTO, GAROSI FRANCO, GAZZI GIORGIO, RIGHINI LUCIANO, TURCHETTI GIANFRANCO, VINCIGUERRA DAMIANO, BOTTICELLI, ANTONIO, CINTI, MARIO, DE ANGELIS, ALBERTO, GAROSI, FRANCO, GAZZI, GIORGIO, RIGHINI, LUCIANO, TURCHETTI, GIANFRANCO, VINCIGUERRA, DAMIANO
Applicants: ENEA ENTE NUOVE TEC, ENEA ENTE PER LE NUOVE TECNOLOGIE, L'ENERGIA E L'AMBIENTE
Application year: 1994
Main classification: G02B5
IPC codes: G02B5